1. Field of the Invention
This invention relates to a hydraulic vibration isolation device and more particularly, to such a hydraulic vibration isolation device that abrupt hydraulic pressure fluctuation between two liquid chambers can be alleviated by flowing the liquid through by opening and dosing of orifices each equipped with a rubber valve.
2. Description of the Related Art
For a hydraulic vibration isolation device of this type, WO 03/033936 A1 discloses the one which comprises an inner cylinder, an outer cylinder, a vibration-isolating base body made of rubber-like elastomer interposed between both cylinders, an intermediate cylinder, a first liquid chamber and a second liquid chamber provided to interpose the inner cylinder on both sides thereof, a main orifice bringing both liquid chambers into communication with each other, a first sub-orifice for flowing the liquid only from the first liquid chamber to the second liquid chamber through a first rubber valve, and a second sub-orifice for flowing the liquid only from the second liquid chamber to the first liquid chamber through a second rubber valve, wherein the intermediate cylinder includes a pair of ring-like fitting peripheral walls on axially both ends thereof to which the outer cylinder is fitted, and a pair of joining walls situated to interpose the center axis of the intermediate cylinder and joining the pair of fitting peripheral walls, and the first sub-orifice and the second sub-orifice are formed on sides of outer peripheral surfaces of the joining walls.
In this hydraulic vibration isolation device, when the hydraulic pressure difference between the first liquid chamber and the second liquid chamber is below a preset value, the first rubber valve and the second rubber valve retain a dosing state and the liquid fluidizes within the main orifice, by fluidization action of which a damping force is exhibited and vibration is absorbed. On the other hand, when the hydraulic pressure difference reaches the preset value and for instance, the hydraulic pressure on the first liquid chamber side is higher, the first rubber valve is resiliently deformed to open owing to the hydraulic pressure and the liquid flows through the second sub-orifice from the second liquid chamber to the first liquid chamber. Thereby the hydraulic pressure of the second liquid chamber is depressed and durability of the rubber wall forming the second liquid chamber is prevented from lowering.
Heretofore the aforesaid main orifice has been configured merely by forming an orifice channel in the rubber portion provided on each of the outer peripheral face sides of the joining walls and covering the orifice channel with the outer cylinder.
According to the conventional configuration described above, because the main orifice was provided on the outer peripheral face sides of the joining walls of the intermediate cylinder, it was difficult to ensure a sufficient orifice length accommodated to the vibration isolating characteristics as required. In particular, with the above-mentioned vibration isolating device, the first sub-orifice and the second sub-orifice as well as the main orifice were formed on the outer peripheral surfaces of the joining walls and consequently, it was unable to ensure a sufficient space to form the main orifice.